Lithographic apparatus

This application claims priority and benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/071,161, entitled “Lithographic Apparatus”, filed on Apr. 16, 2008, the contents of that application incorporated herein in its entirety by reference.

The present invention relates to a lithographic apparatus for providing a fluid to a space between a projection system of an immersion lithographic apparatus and a substrate.

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. In an embodiment, the liquid is distilled water, although another liquid can be used. An embodiment of the present invention will be described with reference to liquid. However, another fluid may be suitable, particularly a wetting fluid, an incompressible fluid and/or a fluid with higher refractive index than air, desirably a higher refractive index than water. Fluids excluding gases are particularly desirable. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. (The effect of the liquid may also be regarded as increasing the effective numerical aperture (NA) of the system and also increasing the depth of focus.) Other immersion liquids have been proposed, including water with solid particles (e.g. quartz) suspended therein, or a liquid with a nano-particle suspension (e.g. particles with a maximum dimension of up to 10 nm). The suspended particles may or may not have a similar or the same refractive index as the liquid in which they are suspended. Other liquids which may be suitable include a hydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueous solution.

Submersing the substrate and/or substrate table in a bath of liquid (see, for example, U.S. Pat. No. 4,509,852) means that there is a large body of liquid that must be accelerated during a scanning exposure. This requires additional or more powerful motors and turbulence in the liquid may lead to undesirable and unpredictable effects.

One of the arrangements proposed is for a liquid supply system to provide liquid on only a localized area of the substrate and in between the final element of the projection system and the substrate using a liquid confinement system (the substrate generally has a larger surface area than the final element of the projection system). One way which has been proposed to arrange for this is disclosed in PCT patent application publication no. WO 99/49504. As illustrated in FIGS. 2 and 3, liquid is supplied by at least one inlet IN (‘N’) onto the substrate, preferably along the direction of movement of the substrate relative to the final element, and is removed by at least one outlet OUT (‘T’) after having passed under the projection system. That is, as the substrate is scanned beneath the element in a −X direction, liquid is supplied at the +X side of the element and taken up at the −X side. FIG. 2 shows the arrangement schematically in which liquid is supplied via inlet IN and is taken up on the other side of the element by outlet OUT which is connected to a low pressure source. In the illustration of FIG. 2 the liquid is supplied along the direction of movement of the substrate relative to the final element, though this does not need to be the case. Various orientations and numbers of in- and out-lets positioned around the final element are possible, one example is illustrated in FIG. 3 in which four sets of an inlet with an outlet on either side are provided in a regular pattern around the final element.

A further immersion lithography solution with a localized liquid supply system is shown in FIG. 4. Liquid is supplied by two groove inlets IN (‘N’) on either side of the projection system PL and is removed by a plurality of discrete outlets OUT (‘T’) arranged radially outwardly of the inlets IN. The inlets IN and OUT can be arranged in a plate with a hole in its center and through which the projection beam is projected. Liquid is supplied by one groove inlet IN on one side of the projection system PL and removed by a plurality of discrete outlets OUT on the other side of the projection system PL, causing a flow of a thin film of liquid between the projection system PL and the substrate W. The choice of which combination of inlet IN and outlets OUT to use can depend on the direction of movement of the substrate W (the other combination of inlet IN and outlets OUT being inactive).

Another arrangement which has been proposed is to provide the liquid supply system with a liquid confinement member which extends along at least a part of a boundary of the space between the final element of the projection system and the substrate table. Such an arrangement is illustrated in FIG. 5. The liquid confinement member is substantially stationary relative to the projection system in the XY plane though there may be some relative movement in the Z direction (in the direction of the optical axis). A seal is formed between the liquid confinement and the surface of the substrate. In an embodiment, a seal is formed between the liquid confinement structure and the surface of the substrate and may be a contactless seal such as a gas seal. Such a system is disclosed in United States patent application publication no. US 2004-0207824, hereby incorporated in its entirety by reference.

In European patent application publication no. EP 1420300 and United States patent application publication no. US 2004-0136494, each hereby incorporated in their entirety by reference, the idea of a twin or dual stage immersion lithography apparatus is disclosed. Such an apparatus is provided with two tables for supporting a substrate. Leveling measurements are carried out with a table at a first position, without immersion liquid, and exposure is carried out with a table at a second position, where immersion liquid is present. Alternatively, the apparatus has only one table.

PCT patent application publication WO 2005/064405 discloses an all wet arrangement in which the immersion liquid is unconfined. In such a system the whole top surface of the substrate is covered in liquid. This may be advantageous because then the whole top surface of the substrate is exposed to the substantially same conditions. This has an advantage for temperature control and processing of the substrate. In WO 2005/064405, a liquid supply system provides liquid to the gap between the final element of the projection system and the substrate. That liquid is allowed to leak over the remainder of the substrate. A barrier at the edge of a substrate table prevents the liquid from escaping so that it can be removed from the top surface of the substrate table in a controlled way. Although such a system improves temperature control and processing of the substrate, evaporation of the immersion liquid may still occur. One way of helping to alleviate that problem is described in United States patent application publication no. US 2006/119809 in which a member is provided which covers the substrate W in all positions and which is arranged to have immersion liquid extending between it and the top surface of the substrate and/or substrate table which holds the substrate.

If a flow of fluid in the space between the final end of the projection system and the substrate is provided, this helps ease the difficulties associated with maintaining a substantially constant temperature of the substrate. This is because the projection beam passing through the immersion fluid can heat the immersion fluid. Such heating can have deleterious effects on the imaging. For example, the refractive index of the fluid can change with temperature. Therefore providing a flow of fluid is desirable. However, the introduction of a flow of fluid may itself introduce difficulties. For example, if non-laminar or non-smooth flow is used, this may affect imaging properties. Furthermore or alternatively, if the stability and robustness of the flow deteriorates, bubbles of gas may be entrained in the fluid.

Furthermore, weld lines between an extractor on the bottom surface of a barrier member and the barrier member itself may attract liquid droplets. Droplets may be left behind on the surface of the substrate. Such droplets could later on introduce image defects, for example by introducing bubbles into the space between the final element of the projection system and the substrate.

It is desirable to provide an apparatus in which at least one of the above, or other, problems are alleviated. In particular, it is desirable to provide a fluid supply system which is capable of supplying fluid at a high flow rate whilst maintaining smooth flow, desirably laminar flow. Furthermore, it is desirable to reduce the chances of droplets being attached to the bottom of a barrier member.

According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising a fluid handling system for supplying a fluid, the fluid handling system comprising: a chamber with a plurality of inlet holes in a first side wall and a plurality of outlet holes in a second side wall, the first side wall facing the second side wall, wherein the inlet holes are arranged to direct fluid entering the chamber in a direction towards areas of the second side wall between the plurality of outlet holes.

According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising a fluid handling system for supplying a fluid, the fluid handling system comprising: a first plate with a plurality of through holes for passage therethrough of fluid; and a second plate with a plurality of through holes for passage therethrough of fluid, wherein the first and second plates are substantially parallel and fluid supplied by the fluid handling system is arranged to pass through the plurality of through holes in the first plate prior to passing through the plurality of holes in the second plate.

According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising a fluid handling system for supplying a fluid, the fluid handling system comprising: a flow passageway from an inlet to an outlet; and at least two barriers for flow present in the passageway, each barrier comprising a plurality of through holes for passage of fluid therethrough, the two barriers being separated by between 0.2 and 5 mm.

According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising a fluid handling system for supplying a fluid, the fluid handling system comprising: a chamber with a plurality of inlet holes in a first side wall and a plurality of outlet holes in second side wall, the plurality of inlet holes having a smaller opening dimension than the plurality of outlet holes.

According to an aspect of the invention there is provided an immersion lithographic apparatus comprising a fluid handling system for supplying a fluid through an inlet, the inlet comprising: at least two spaced-apart plate members facing each other and each having a plurality of through holes, wherein for the flow of fluid through the inlet the through holes of one plate member are non-aligned with the through holes of another plate member.